[show abstract][hide abstract] ABSTRACT: Monitoring bacteria growth and motion in environments is fundamental to understand, for instance, how they proliferate and contaminate organism. Therefore, techniques to fabricate microenvironments for in situ and in vivo studies are interesting for that purpose. In this work we used two-photon polymerization to fabricate microenvironments and, as a proof of principle, we demonstrated the development of the bacteria ATCC 25922 Escherichia coli (E. coli) into the microstructure surroundings. Two varieties of polymeric microenvironments are presented: (i) a microenvironment doped at specific site with ciprofloxacin, an antibiotic typically used in the treatment of diseases caused by E. coli and (ii) micro-fences, which serve as traps for bacteria. These microenvironments, fabricated by two-photon polymerization, may be a potential platform for drug delivery system, by promoting or inhibiting the growth of bacteria in specific biological or synthetic sites.
Materials Science and Engineering: C. 01/2014; 35:185–189.
[show abstract][hide abstract] ABSTRACT: This work demonstrated the fabrication of tubular waveguides in bulk samples of PMMA doped with Disperse Red 13 (DR13) by oscillator only fs-laser micromachining. We studied the influence of the incident pulse energy on the diameter and quality of the fabricated waveguides by analyzing optical microscopy images. HeNe laser (632.8 nm) was coupled into the fabricated waveguides, revealing an annular intensity distribution resulting from the superposition of propagation modes with azimuthal symmetry. The averaged total loss of the fabricated waveguides was estimated as 0.8 dB/mm. Residual birefringence was observed in the produced waveguides, probably generated during the fabrication process, which prevented determining optically induced birefringence owing to the presence of the azochromophore DR13.
[show abstract][hide abstract] ABSTRACT: a b s t r a c t We propose a combination of different techniques to obtain the absorption cross-section spectra of trip-let-and singlet-states in porphyrin-like molecules. Two extensions of the Z-scan technique are employed (pulse train Z-scan and white-light Z-scan) together with absorbance spectroscopy and laser flash pho-tolysis. This approach allowed us to investigate features of excited-states absorption of meso-tetrakis (methylpyridiniumyl) porphyrin (TMPyP) that revealed the influence of solvents on the vibronic structur-ation of the transitions assigned to triplet-states, probably caused by hydrogen bonds established between the porphyrin and solvent molecules. Ó 2013 Elsevier B.V. All rights reserved.
Chemical Physics Letters 11/2013; 587:118–123. · 2.15 Impact Factor
[show abstract][hide abstract] ABSTRACT: Tailoring properties of materials by femtosecond laser processing has been proposed in the last decade as a powerful approach for technological applications, ranging from optics to biology. Although most of the research output in this field is related to femtosecond laser processing of single either organic or inorganic materials, more recently a similar approach has been proposed to develop advanced hybrid nanomaterials. Here, we report results on the use of femtosecond lasers to process hybrid nanomaterials, composed of polymeric and glassy matrices containing metal or semiconductor nanostructures. We present results on the use of femtosecond pulses to induce Cu and Ag nanoparticles in the bulk of borate and borosilicate glasses, which can be applied for a new generation of waveguides. We also report on 3D polymeric structures, fabricated by two-photon polymerization, containing Au and ZnO nanostructures, with intense two-photon fluorescent properties. The approach based on femtosecond laser processing to fabricate hybrid materials containing metal or semiconductor nanostructures is promising to be exploited for optical sensors and photonics devices.
[show abstract][hide abstract] ABSTRACT: We report on the control of multi-photon excited emission of the ZnO exciton band via spectral phase modulation of the femtosecond excitation pulses. It was observed that the optimum spectral phase that enhances the exciton emission results in a pulse-train temporal profile, whose separation corresponds to an energy of 82 meV, which is close to the energy of LO phonon sidebands in ZnO emission. Such a result suggests that exciton–LO phonon coupling can be explored to coherently enhance the exciton emission in ZnO single crystals with respect to the defect luminescence band.
[show abstract][hide abstract] ABSTRACT: In this work, we designed and recorded two-dimensional Hexagonal
Photonic Crystals (2D-HPC) layers, with a linear waveguide, in erbium
glassy films, by combining the techniques of holographic recording and
femtosecond (fs) laser micromachining. The 2D-HPC is recorded
holographically in a photoresist film coated on a glass substrate by
exposing the sample to the same interference pattern twice and rotating
the sample of 60° between the exposures. After the development a two
dimensional hexagonal array of photoresist columns remain on the glass
substrate. The recording of the waveguide is made by a fs laser
micromachining system focused at sample surface. The laser spot produces
the ablation of the photoresist columns generating a defect line in the
periodic hexagonal array. After the recording of the photoresist
template, the erbium doped
GeO2-Bi2O3-PbO-TiO2 film is
evaporated on the photoresist and finally the photoresist template is
removed using acetone. The design of the geometrical parameters of the
2D-HPC is performed by calculation of the dispersion mode curves of the
photonic crystal using a 2D finite element method. The proper
geometrical parameters depend on both the refractive index of the glass
film and thickness. Such parameters as well as the period of the 2D-HPC
have been defined in order to obtain a photonic band gap in the region
of erbium luminescence band. In such condition the erbium luminescence
will propagate only through the waveguide.
[show abstract][hide abstract] ABSTRACT: This work reports on the photophysical properties of zinc porphyrins meso-tetrakis methylpyridiniumyl (Zn(2+)TMPyP) and meso-tetrakis sulfonatophenyl (Zn(2+)TPPS) in homogeneous aqueous solutions and in the presence of sodium dodecyl sulfate (SDS) and cetyltrimethyl ammonium bromide (CTAB) micelles. The excited-state dynamic was investigated with the Z-scan technique, UV-Vis absorption, and fluorescence spectroscopy. Photophysical parameters were obtained by analyzing the experimental data with a conventional five-energy-level diagram. The interaction of the charged side porphyrin groups with oppositely charged surfactants can reduce the electrostatic repulsion between porphyrin molecules leading to aggregation, which affected the porphyrin characteristics such as absorption cross-sections, lifetimes and quantum yields. The interaction between anionic ZnTPPS with cationic CTAB micelles induced the formation of porphyrin J-aggregates, while this effect was not observed in the interaction of ZnTMPyP with SDS micelles. This difference is, probably, due to the difference in electrostatic repulsion between the porphyrin molecules. The insights obtained by these results are important for the understanding of the photophysical behavior of porphyrins, regarding potential applications in pharmacokinetics as encapsulation of photosensitizer for drug delivery systems and in its interaction with cellular membrane.
Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 04/2013; 112C:309-317. · 1.98 Impact Factor
[show abstract][hide abstract] ABSTRACT: Birefringent materials have many applications in optical devices. An approach to obtain optically induced birefringence is to employ a guest-host strategy, using a polymer matrix containing an azodye. However, such method normally leads to low residual birefringence. Therefore, methodologies to produce microstructures with optimized birefringence are still on demand. Here we report on the fabrication, using two-photon polymerization, and characterization of birefringent microstructures produced in a polymer blend containing an azopolymer. Such microstructures present good structural integrity and residual birefringence of approximately 35 percent, depending on the sample formulation used, which indicates this approach for the fabrication of microoptical devices. (C) 2012 Optical Society of America
[show abstract][hide abstract] ABSTRACT: We report the control of Au nanoparticle (NP) formation by using shaped 30 fs pulses, in a solution containing HAuCl4 and chitosan. By using a sinusoidal spectral phase, a periodic train of pulses is generated. When the period of the pulse train matches certain Raman resonances of chitosan, the reducing agent of the process, an enhancement of the Au NP formation is observed. Theoretical quantum chemical calculations indicate that the outer groups of the chitosan are mostly influenced by low Raman frequencies, which is in reasonably agreement with the experimental data and indicates an enhancement in the Au NP formation as the pulse train period increases (low frequency).
[show abstract][hide abstract] ABSTRACT: In this report, we investigate the polarization effect (linear, elliptical and circular) on the two-photon absorption (2PA) properties of a chiral compound based in azoaromatic moieties using the femtosecond Z-scan technique with low repetition rate and low pulse energy. We observed a strong 2PA modulation between 800 nm and 960 nm as a function the polarization changes from linear through elliptical to circular. Such results were interpreted employing the sum-over-essential states approach, which allowed us to model the 2PA circular-linear dichroism effect and to identifier the overlapping of the excited electronic states responsible by the 2PA allowed band.
[show abstract][hide abstract] ABSTRACT: Glasses containing metallic nanoparticles are promising materials for technological applications in optics and photonics. Although several methods are available to generate nanoparticles in glass, only femtosecond lasers allow controlling it three-dimensionally. In this direction, the present work investigates the generation of copper nanoparticles on the surface and in the bulk of a borosilicate glass by fs-laser irradiation. We verified the formation of copper nanoparticles, after heat treatment, by UV-Vis absorption, transmission electron microscopy and electron diffraction. A preferential growth of copper nanoparticles was observed in the bottom of the irradiated region, which was attributed to self-focusing in the glass.
[show abstract][hide abstract] ABSTRACT: In this report, we investigate the influence of temperature on the two-photon absorption (2PA) spectrum of all-trans-β-carotene using the femtosecond white-light-continuum Z-scan technique. We observed that the 2PA cross-section decreases quadratically with the temperature. Such effect was modeled using a three-energy-level diagram within the sum-over-essential states approach, assuming temperature dependencies to the transition dipole moment and refractive index of the solvent. The results show that the transition dipole moments from ground to excited state and between the excited states, which governed the two-photon matrix element, have distinct behaviors with the temperature. The first one presents a quadratic dependence, while the second exhibits a linear dependence. Such effects were attributed mainly to the trans→cis thermal interconversion process, which decreases the effective conjugation length, contributing to diminishing the transition dipole moments and, consequently, the 2PA cross-section.
The Journal of Physical Chemistry A 06/2012; 116(26):7033-8. · 2.77 Impact Factor
[show abstract][hide abstract] ABSTRACT: a b s t r a c t Experimental and theoretical studies on the two-photon absorption properties of two oxazole deriva-tives: 2,5-diphenyloxazole (PPO) and 2-(4-biphenylyl)-5-phenyl-1,3,4-oxadiazole (PBD) are presented. The two-photon absorption cross-section spectra were determined by means of the Z-scan technique, from 460 up to 650 nm, and reached peak values of 84 GM for PBD and 27 GM for PPO. Density Functional Theory and response function formalism are used to determine the molecular structures and the one-and two-photon absorption properties and to assist in the interpretation of the experimental results. The Polarizable Continuum Model in one-photon absorption calculations is used to estimate solvent effects.
[show abstract][hide abstract] ABSTRACT: This paper reports the synthesis of Au nanoparticles by 30-fs pulses irradiation of a sample containing HAuCl4 and chitosan, a biopolymer used as reducing agent and stabilizer. We observed that it is a multi-photon induced process, with a threshold irradiance of 3.8 × 10(11) W/cm2 at 790 nm. By transmission electron microscopy we observed nanoparticles from 8 to 50 nm with distinct shapes. Infrared spectroscopy indicated that the reduction of gold and consequent production of nanoparticles is related to the fs-pulse induced oxidation of hydroxyl to carbonyl groups in chitosan.
[show abstract][hide abstract] ABSTRACT: The use of laser light to modify the material's surface or bulk as well as to induce changes in the volume through a chemical reaction has received great attention in the last few years, due to the possibility of tailoring the material's properties aiming at technological applications. Here, we report on recent progress of microstructuring and microfabrication in polymeric materials by using femtosecond lasers. In the first part, we describe how polymeric materials' micromachining, either on the surface or bulk, can be employed to change their optical and chemical properties promising for fabricating waveguides, resonators, and self-cleaning surfaces. In the second part, we discuss how two-photon absorption polymerization can be used to fabricate active microstructures by doping the basic resin with molecules presenting biological and optical properties of interest. Such microstructures can be used to fabricate devices with applications in optics, such as microLED, waveguides, and also in medicine, such as scaffolds for tissue growth.
IEEE Journal of Selected Topics in Quantum Electronics 01/2012; 18(1):176-186. · 4.08 Impact Factor
[show abstract][hide abstract] ABSTRACT: Fabrication of microstructures containing active compounds, such as fluorescent dyes and nanoparticles have been exploited in the last few years, aiming at applications from photonics to biology. Here we fabricate, using two-photon polymerization, microstructures containing the fluorescent dyes Stilbene 420, Disodium Fluorescein and Rhodamine B. The produced microstructures, containing dyes at specific sites, present good structural integrity and a broad fluorescence spectrum, from about 350 nm until 700 nm. Such spectrum can be tuned by using different excitation wavelengths and selecting the excitation position in the microstructure. These results are interesting for designing multi-doped structures, presenting tunable and broad fluorescence spectrum. (C)2012 Optical Society of America
[show abstract][hide abstract] ABSTRACT: In this article, we investigate the linear and nonlinear optical properties of the thiophene/phenylene-based oligomer (SL128G) and polymer (FSE59) chemically modified with alquilic chains, which allow greater solubility and provide new optical properties. These compounds present a strong absorption in the UV-visible region, providing a wide transparence window in visible-IR, ideal for applications in nonlinear optics. Employing the Z-scan technique with femtosecond pulses, we show that these compounds exhibit considerable two-photon absorption (2PA), with two 2PA allowed states located at 650 and 800 nm for SL128G and 780 and 920 nm for FSE59. Moreover, we observe the resonance enhancement effect as the excitation wavelength approaches the lowest one-photon-allowed state. By modeling the 2PA spectra considering a four-energy-level diagram within of the sum-over-essential states approach, we obtained the spectroscopic parameters of the electronic transitions to low-energy singlet excited states. Additionally, photoluminescence excited by femtosecond and picosecond pulses were performed to confirm the order of the multiphoton process and estimate the fluorescence lifetime, respectively.
The Journal of Physical Chemistry B 11/2011; 115(44):12687-93. · 3.61 Impact Factor
[show abstract][hide abstract] ABSTRACT: We have determined two-photon absorption and nonlinear refraction spectra of the 50BO(1.5) - (50-x)PbF(2) - xPbO glasses (with x = 25, 35, 50 cationic %) at the range of the 470 and 1550 nm. The replacement of fluor atoms by oxygen leads to an increase in the third-order susceptibility, due to the formation of non-bridging oxygens (NBO). The nonlinear index of refraction is one order of magnitude higher than the one for fused silica, and it increases almost twice for the sample with x = 50. This sample has also shown promising features for all-optical switching as well as for optical limiting.
[show abstract][hide abstract] ABSTRACT: This work demonstrates that the detuning of the fs-laser spectrum from the two-photon absorption band of organic materials can be used to reach further control of the two-photon absorption by pulse spectral phase manipulation. We investigate the coherent control of the two-photon absorption in imidazole–thiophene core compounds presenting distinct two-photon absorption spectra. The coherent control, performed using pulse phase shaping and genetic algorithm, exhibited different growth rates for each sample. Such distinct trends were explained by calculating the two-photon absorption probability considering the intrapulse interference mechanism, taking into account the two-photon absorption spectrum of the samples. Our results indicate that tuning the relative position between the nonlinear absorption and the pulse spectrum can be used as a novel strategy to optimize the two-photon absorption in broadband molecular systems.